rearsensor
nounUK /ˈrɪəˌsɛnsə/
US /ˈrɪrˌsɛnsər/
A rear sensor is a small device on the back of a car that helps you know when something is close behind.
The rear sensor beeped when I backed the car toward the garage door.
OTHER MEANINGS
2. A sensor mounted at the rear of a machine to detect movement or objects behind it.
The robot's rear sensor stopped it from bumping into the wall.
3. A device on the back of a phone or camera that detects light or motion.
The rear sensor on the phone helps take clearer pictures in low light.
4. A detector placed behind a door or gate to notice people approaching from the back.
The rear sensor opened the gate when the delivery truck pulled up.